In the existing image display technologies, TFT liquid crystal display devices have distinguished themselves in virtue of their excellent properties, and have been widely used in various areas such as cell phones, computers, televisions, etc. Liquid crystal display devices achieve display of images by controlling transmittance of backlight source through causing non-luminous liquid crystal to deflect under the influence of voltage, and therefore, backlight module is an important part of liquid crystal display devices.
Currently, most of manufactures adopt an LED backlight system as shown in FIG. 1 as the backlight source of a liquid crystal display panel. This LED backlight system mainly comprises a power supply unit 110, a plurality of LED light strips 120, a booster unit 130 which is electrically connected between the power supply unit 110 and the plurality of LED light strips 120, and a driving chip 140 which is electrically connected between a plurality of the LED light strips 120 and the booster unit 130. The driving chip 140, on the one hand, based on a current and a voltage fed back by the LED light strips, transmits a gate control signal Vmos to a transistor 131 in the booster unit 130, for regulating a driving voltage Vout supplied by the power supply unit 110 to the LED light strips 120 through the booster unit 130, and on the other, based on the current and the voltage fed back by the LED light strips, regulates currents Iled flowing through the LED light strips 120 (i.e., regulating the brightness of the LED lights) by modulating PWM duty ratio under the influence of an operating voltage Va.
In addition, the driving chip 140 is also able to detect failure of the LED light strips. Specifically, the driving chip detects voltages on negative ends of the LED light strips (i.e., detecting a difference between the driving voltage Vout and a voltage actually needed by the LED light strips). When a certain LED light strip fails so that a voltage on the negative end thereof is higher than a predetermined threshold voltage, the driving chip will activate a self-protection function and thus cut off its electrical connection to said LED light strip. Usually, the threshold voltage is a set value of the driving chip, which is often one of 3V, 6V, 9V or 12V.
However, the inventor found through repeated observations that the above driving chip often provides wrong judgments in practice. This is because the LED light strips may have different electrical properties, and may actually require different voltages when a same current flows through them, which causes voltages on the negative ends of each of the LED light strips to be different. For example, if an LED light strip has a small resistance, and it can work normally but a voltage on its negative end is higher than the threshold voltage, the driving chip will activate the protection function and then cut off its electrical connection to said LED light strip. Or, if an LED light strip fails, but a voltage on its negative end is not higher than the threshold voltage, the driving chip will not activate the protection function. In particular, if there is only one LED light in an LED light strip that is short-circuited or virtually off, it will be very difficult for the driving chip to identify the failure because the voltage on its negative end will not vary much and will not be higher than the threshold voltage. In addition, due to the obstruction of fittings such as the light guide plate and films disposed within the backlight module, it will also be difficult to detect the failure manually. Thus, the circuit abnormity will continue to be present and become worse, thereby causing safety problems.